1. Field of the Invention
The present invention relates to a direction and position finding apparatus which receives radio wave and determines the direction of arrival and the position of the emission source thereof with high accuracy.
2. Description of the Prior Art
One of the well-known prior basic direction finding apparatuses to detect the direction of arrival of radio wave is, for example, Yagi antenna which detects the direction of arrival of the radio wave using a directional antenna. Another direction finding apparatus is disclosed in the Japanese Patent Application No. H3-67789, which uses a non-directional antenna and a directional antenna to determine the direction. These conventional types of detection apparatuses provide a system to assume an azimuth angle using the directional characteristic of the antenna.
However, as conventional direction finding apparatuses are constructed as mentioned above, the accuracy of finding direction of the maximum received electric power is limited to +/xe2x88x9210 to 20 degrees due to a half value angle of a directional antenna (a beam spread angle at a half of the peak electric power (xe2x88x923 dB)). Therefore, high accuracy detection has not been obtained.
The present invention is made to solve the problems described above, and an object thereof is to provide a direction and position finding apparatus capable of not only detecting the direction of arrival of radio wave with high accuracy, but also performing a highly accurate position finding of the emission source thereof, in other words, to provide a direction and position finding apparatus capable of performing detection of both the direction of arrival and the emission source of radio wave with a higher accuracy than used to be.
In order to accomplish the object, the radio direction and position finding apparatus in accordance with the present invention comprises; a first directional antenna which rotates with a desired angle of elevation; a first phase integral means for producing an output through an integration of output from the first directional antenna; a first phase difference means for producing an output as a difference of the outputs from the first directional antenna; a first frequency dividing means for dividing frequency of integral component of the output from the first directional antenna; a first differential gain control means for controlling gain of differential component of the output from the first directional antenna; a first receiving means for receiving output from the first frequency dividing means and producing a detection signal output; a second receiving means for receiving output from the first differential gain control means and producing a detection signal output; a first subtraction means for subtracting one detection signal output from the other detection signal output of the first and the second receiving means; a first calculation means for determining a direction of arrival of radio wave based on output from the first subtraction means; a second directional antenna which rotates with a desired angle of elevation; a second phase integral means for producing an output through an integration of output from the second directional antenna; a second phase difference means for producing an output as a difference of outputs from the second directional antenna; a second frequency dividing means for dividing frequency of integral component of the output from the second directional antenna; a second differential gain control means for controlling differential component of the output from the second directional antenna; a third receiving means for receiving output from the second frequency dividing means and producing a detection signal output; a fourth receiving means for receiving output from the second differential gain control means and producing a detection signal output; a second subtraction means for subtracting one detection signal output from the other detection signal output of the third and the fourth receiving means; a second calculation means for determining a direction of arrival of radio wave based on output from the second subtraction means; and a position determining calculation means for determining the position of the emission source of the radio wave based on outputs from the first and the second calculation means; wherein the first directional antenna and the second directional antenna rotate interlockingly.
With the arrangements described above, it is possible to detect the direction of arrival of the radio wave with a high accuracy and specify the position of the emission source of the radio wave with high accuracy.
According to the radio direction and position finding apparatus of the present invention, each of the first and the second directional antennas may use at least two vertical polarized waves.
With this arrangement, it is possible to determine the direction and the position of the emission source of the radio wave based on the integral output and the differential output of two vertical polarized directional antenna patterns. The term xe2x80x9cantenna patternxe2x80x9d as used herein means received signals corresponding respectively to the horizontal plane and the vertical plane of each of the directional antennas.
According to the radio direction and position finding apparatus of the present invention, one of the first and the second directional antennas may use a vertical polarized radio wave with acute horizontal directivity, and the other of the first and the second directional antennas may use a vertical polarized radio wave with acute vertical directivity.
With this arrangement, it is possible to determine the direction of arrival and the position of the emission source of the radio wave based on the integral output and the differential output of the antenna pattern of one-column two-row vertical polarized wave directional antenna and the integral output and the differential output of the antenna pattern of two-column one-row vertical polarized wave directional antenna.
According to the radio direction and position finding apparatus of the present invention, the phase integral means may be constructed to integrate the strength of electrical field component received at the first and the second directional antennas.
With this arrangement, signals of the same frequency are integrated so that it is possible to intensify the same phase components and detect more accurately the direction of the emission source of the radio wave.
According to the radio direction and position finding apparatus of the present invention, the phase difference means may be constructed to be capable of setting the phase difference based on outputs from the first and the second directional antennas in providing the difference.
Thus, it becomes possible to detect the direction of the emission source of the radio wave based on the differential output as obtained from the outputs of the directional antennas by offsetting the phase differences.
According to the present invention, the radio direction and position finding apparatus may be provided with means for controlling the gain of the differential component of the output from each of the first and the second directional antennas to thereby determine the position of the emission source of the radio wave.
The apparatus constructed as described above can determine the direction of arrival of the radio wave by interlockingly rotating the two directional antennas to maximize the integral output and also determine the position of the emission source of the radio wave by controlling the angle of elevation while controlling the gain of the differential output.